mirror of
https://github.com/MichaelMure/git-bug.git
synced 2024-12-15 02:01:43 +03:00
89 lines
2.6 KiB
Go
89 lines
2.6 KiB
Go
/*
|
|
|
|
This Source Code Form is subject to the terms of the Mozilla Public
|
|
License, v. 2.0. If a copy of the MPL was not distributed with this file,
|
|
You can obtain one at http://mozilla.org/MPL/2.0/.
|
|
|
|
Copyright (c) 2013, Armon Dadgar armon.dadgar@gmail.com
|
|
Copyright (c) 2013, Mitchell Hashimoto mitchell.hashimoto@gmail.com
|
|
|
|
Alternatively, the contents of this file may be used under the terms
|
|
of the GNU General Public License Version 3 or later, as described below:
|
|
|
|
This file is free software: you may copy, redistribute and/or modify
|
|
it under the terms of the GNU General Public License as published by the
|
|
Free Software Foundation, either version 3 of the License, or (at your
|
|
option) any later version.
|
|
|
|
This file is distributed in the hope that it will be useful, but
|
|
WITHOUT ANY WARRANTY; without even the implied warranty of
|
|
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General
|
|
Public License for more details.
|
|
|
|
You should have received a copy of the GNU General Public License
|
|
along with this program. If not, see http://www.gnu.org/licenses/.
|
|
|
|
*/
|
|
|
|
package lamport
|
|
|
|
import (
|
|
"sync/atomic"
|
|
)
|
|
|
|
// Clock is a thread safe implementation of a lamport clock. It
|
|
// uses efficient atomic operations for all of its functions, falling back
|
|
// to a heavy lock only if there are enough CAS failures.
|
|
type Clock struct {
|
|
counter uint64
|
|
}
|
|
|
|
// Time is the value of a Clock.
|
|
type Time uint64
|
|
|
|
// NewClock create a new clock with the value 1.
|
|
// Value 0 is considered as invalid.
|
|
func NewClock() Clock {
|
|
return Clock{
|
|
counter: 1,
|
|
}
|
|
}
|
|
|
|
// NewClockWithTime create a new clock with a value.
|
|
func NewClockWithTime(time uint64) Clock {
|
|
return Clock{
|
|
counter: time,
|
|
}
|
|
}
|
|
|
|
// Time is used to return the current value of the lamport clock
|
|
func (l *Clock) Time() Time {
|
|
return Time(atomic.LoadUint64(&l.counter))
|
|
}
|
|
|
|
// Increment is used to return the value of the lamport clock and increment it afterwards
|
|
func (l *Clock) Increment() Time {
|
|
return Time(atomic.AddUint64(&l.counter, 1) - 1)
|
|
}
|
|
|
|
// Witness is called to update our local clock if necessary after
|
|
// witnessing a clock value received from another process
|
|
func (l *Clock) Witness(v Time) {
|
|
WITNESS:
|
|
// If the other value is old, we do not need to do anything
|
|
cur := atomic.LoadUint64(&l.counter)
|
|
other := uint64(v)
|
|
if other < cur {
|
|
return
|
|
}
|
|
|
|
// Ensure that our local clock is at least one ahead.
|
|
if !atomic.CompareAndSwapUint64(&l.counter, cur, other+1) {
|
|
// CAS: CompareAndSwap
|
|
// The CAS failed, so we just retry. Eventually our CAS should
|
|
// succeed or a future witness will pass us by and our witness
|
|
// will end.
|
|
goto WITNESS
|
|
}
|
|
}
|